This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-37789 filed on Feb. 16, 2000.
1. Field of the Invention
The present invention relates to an electromagnetic valve for controlling the pressure of a fluid.
2. Description of Related Art
JP-A-10-299932 discloses an electromagnetic valve in which attracting portion of a stator core attracts a moving core when a coil is energized. In the electromagnetic valve, a resin bobbin supports a plunger working as the moving core to allow it to reciprocate thereinside.
However, the resin bobbin is formed independently from a container portion of the stator core, which covers the outer wall of the moving core, so that the axis of the bobbin might deviate from the axis of the container portion. When the axis of the bobbin deviates from the axis of the container portion, the moving core might contact with the container portion to obstruct a reciprocation of the moving core. Thus, an air gap between the moving core and the container portion has to be enlarged for preventing the moving core from contacting the container portion.
However, when the air gap is enlarged, attracting force for attracting the moving core is reduced. For attaining a required attracting force, winding number of the coil has to be increased, thereby enlarging an entire electromagnetic valve.
An object of the present invention is to increase an attracting force for attracting a moving core without enlarging an entire electromagnetic valve.
According to a first aspect of the present invention, a first stator contains and supports a moving core to allow it to reciprocate thereinside. A second stator magnetically attracts the moving core in a reciprocating direction of the moving core. A nonmagnetic member is provided between one end surface of the moving core, which faces the second stator, and the second stator, and is provided between an outside wall of the moving core and the first stator.
Since the thickness of the nonmagnetic member works as an air gap, an attracting force for attracting the moving core is increased by making the thickness of the nonmagnetic member as thin as possible. Further, since the nonmagnetic member is provided between the moving core and the second stator, there is no need to prepare an additional nonmagnetic stopper for preventing the moving core from contacting the second stator.
According to a second aspect of the present invention, the nonmagnetic member is formed in a cylindrical cup. The cylindrical cup-shaped nonmagnetic member is easily press-formed.
Since the cylindrical cup-shaped nonmagnetic member is press-formed, the nonmagnetic member has a uniform thickness, thereby preventing an irregularity of the air gap. Further, the cylindrical cup-shaped nonmagnetic member is easily fit to the moving core. The cylindrical cup-shaped nonmagnetic member may be adhered or welded to the moving core.
According to a third aspect of the present invention, the nonmagnetic member is formed in a cylindrical film. The nonmagnetic cylindrical film is elastically and easily attached to the moving core or the first stator.